The typical prior art exhaust muffler includes a plurality of discrete parallel tubes supported by transversely extending baffles. The tubes and baffles are disposed in a separate tubular outer shell. An outer wrapper may be disposed over the tubular outer shell to dampen vibrations in the shell. Headers or end caps are then affixed to the opposed ends of the tubular outer shell and the wrapper to substantially enclose the opposed ends of the prior art muffler. Each header or end cap of the prior art muffler has at least one aperture to which an exhaust pipe or a tail pipe of a vehicular exhaust system is mounted. Chambers are defined in this prior art muffler by the outer shell and a pair of spaced apart baffles or by the outer shell, one baffle and an end cap or header of the muffler. The tubes of the prior art muffler are disposed and configured to provide communication with the respective chambers. In particular, selected areas of certain tubes may be perforated or louvered to permit an expansion of exhaust gas into the surrounding chamber. Other tubes will terminate or start in a chamber. The particular arrangement and dimensions of components in this prior art muffler are selected in accordance with the acoustical characteristics of the exhaust gas flowing through the muffler, back pressure specifications recommended by the vehicle manufacturer and space limitations on the underside of the vehicle.
A typical prior art muffler is shown in FIG. 10 and is identified generally by the numeral 10. The prior art muffler 10 often is referred to as a tri-flow muffler and includes an inlet tube 12 and outlet tube 14. The inlet tube 12 is supported by an end cap 16 and by baffles 18 and 20 respectively. The outlet tube 14 is supported in parallel relationship to the inlet tube 12 by transverse baffles 18, 20, 22 and 24 and by the end cap 26. A perforated return tube 28 also is supported by the transverse baffles 18 and 20 in generally parallel relationship to the inlet and outlet tubes 12 and 14. A tuning tube 30 is supported by the baffles 22 and 24 and is also parallel to the inlet and outlet tubes 12 and 14. A tubular outer shell 32 encloses the above described end caps and baffles 16-26 and the tubes supported thereby. An outer wrapper 34 is engaged around the shell 32 to minimize vibration and to thereby avoid the shell ring noise associated with such vibrations.
As noted above, the various components of the prior art tri-flow muffler 10 are disposed in accordance with the particular acoustical characteristics of the exhaust gas flow for the vehicle on which the prior art tri-flow muffler 10 is mounted. In this regard, the exhaust gas enters the prior art muffler 10 through the inlet tube 12 and will expand through the perforations 36 to communicate with the expansion chamber 38 defined between the baffles 18 and 20. A substantial portion of the exhaust gas will continue to flow into the reversing chamber 40 defined between the baffles 20 and 22 of the prior art muffler 10. The expansion of exhaust gas enter the reversing chamber contributes to noise attenuation. The amount of attenuation and the frequencies for which attenuation occurs depends in part upon the expansion ratio which relates the cross-sectional dimensions of the tube with the cross-sectional dimensions of the chamber. The tube and chamber dimensions can be selected (to the extent permitted by other design constraints) to achieve a preferred expansion ratio and hence a preferred attenuation. The rapidly flowing exhaust gas creates substantial pressure on the walls of the reversing chamber 40. The forces generate movement and vibration in the baffles 20 and 22 and the shell 32 of the prior art muffler 10 as the gases undergo the 180.degree. change in direction. However, the internal disposition of the reversing chamber 40 insulates and thus dampens any shell ring that could be generated by movement of the walls defining reversing chamber 40. The tuning tube 30 of the prior art muffler 10 is aligned with the inlet tube 12 for an efficient "driven" tuning effect, and then extends into a low frequency resonating chamber 42. The dimensions of the tuning tube 30 and the volume of the low frequency resonating chamber 42 are selected to attenuate a particular narrow band of low frequency noise that may not be adequately attenuated by the other components of the prior art muffler. It will be noted that the low frequency resonating chamber 42 is a dead end chamber. As a result the exhaust gas entering the reversing chamber 40 will flow over and under the outlet tube 14 to enter the return tube 28. Thus, the exhaust gas undergoes a 180.degree. change in direction between the inlet and return tubes. The perforations 44 in the return tube 28 will enable a communication of exhaust gas with the expansion chamber 38. However, a substantial portion of the exhaust gas will continue through the return tube 28 and into the second reversing chamber 46 and from there into the outlet tube 14. The outlet tube 14 is provided with an array of perforations 48 in the expansion chamber 38. As a result, exhaust gas will flow into the outlet tube 14 from both the reversing chamber 46 and the expansion chamber 38. The outlet tube 14 further includes an array of perforations 50 which enable communication with a high frequency tuning chamber 52 defined by the baffles 22 and 24. The perforations 50 and the high frequency tuning chamber 52 both are dimensioned to attenuate a narrow range of high frequency noise that is not adequately attenuated by the other components of the muffler. The exhaust gas will continue through the outlet tube 14 and will communicate with a tail pipe welded or otherwise connected to the outlet tube 14 in proximity to the end cap 26.
Mufflers like the prior art tri-flow muffler 10 of FIG. 10 generally perform well. Despite the efficient performance, however, it will be noted that the prior art muffler 10 requires twelve components which must be assembled in a labor intensive manufacturing process. The assembled prior art muffler 10 must then be connected to the exhaust pipe and tail pipe of the exhaust system by welding or by clamps which generally require additional labor intensive manufacturing steps. The prior art muffler 10 further includes several functional disadvantages. In particular, the abrupt sharp edges of the tubes in the prior art muffler 10 result in less then optimum noise attenuation for at least certain narrow frequency bands, and may generate a secondary "flow noise" within the prior art muffler 10. Similar undesirable results are attributable to the sharp corners and parallel walls defined within the respective chambers of the prior art muffler 10. The prior art muffler 10 may also be difficult to tailor to a particular vehicle within a class of related vehicles. For example, certain vehicles within a class of related vehicles may not require the high frequency tuning chamber 52. However, the removal of the baffle 22 or 24 and the elimination of the perforations 50 necessarily will alter the noise attenuation characteristics of either the low frequency resonating chamber 42 or the reversing chamber 40. Similarly, it may be difficult to alter the low frequency resonating characteristics achieved by the tuning tube 30 and the low frequency resonating chamber 42 without affecting other performance characteristics of the prior art muffler 10. Similarly, if a second low frequency resonating chamber and tuning tube combination were required for a particular vehicle within a class of related vehicles, a substantial re-design of the entire prior art muffler 10 may be required.
Mufflers formed at least in part from stamped components have been available for many years. The typical prior art stamp formed muffler includes a pair of internal plates stamped with channels. The internal plates are secured to one another such that the channels define an array of tubes, portions of which may be perforated, louvered or otherwise configured to permit expansion of exhaust gas from the tubes. The typical prior art stamped muffler will further include a pair of stamp formed external shells surrounding and communicating with the tubes. Stamp formed mufflers generally require many fewer components than the conventional mufflers described and illustrated above. Furthermore, stamp formed mufflers can be manufactured in processees that are well suited for a high degree of automation. Until recently, however, the prior art stamp formed mufflers were not completely effective in attenuating the full range of noise associated with the flow of exhaust gas. In particular, the typical prior art stamp formed muffler had merely included perforated tubes passing through one or more expansion chambers. There was no accommodation for the narrow ranges of low frequency noise or high frequency noise that may not have been adequately attenuated by the simple combination of a perforated tube passing through an expansion chamber. Examples of prior art mufflers of this general type include U.S. Pat. No. 3,140,750 which issued to Tranel on Jul. 14, 1964 and U.S. Pat. No. 4,396,090 which issued to Wolfhungel on Aug. 2, 1984. U.K. Published Patent Application No. 2,120,318 shows a stamp formed tri-flow muffler with reversing chambers at opposed ends of the muffler and an expansion chamber therebetween.
Some prior art mufflers have included short conventional tubular components and/or separate baffles in combination with various stamped components in an effort to enhance the tuning options, and thereby improve the acoustical performances of the muffler. An example of a tri-flow muffler formed with both stamped and conventional tubular components is shown in U.S. Pat. No. 5,012,891 which issued to Macaluso on May 7, 1991. The reversing or turn-around chamber of U.S. Pat. No. 5,012,891 is at one longitudinal end of the muffler and is defined by the external shell. In some instances this leads to excessive vibration of the external shell. Furthermore, U.S. Pat. No. 5,012,891 indicates that a resonating chamber or Helmholtz chamber is not intended for a muffler of the type disclosed therein, since excessive noise is considered an attribute to suggest "power". Other mufflers with stamped and conventional components are shown in Japanese Published Patent Application No. 2-207124; and Japanese Published Utility Model Applications No. 2-83324 and No. 2-83317. These references do not show tuning tubes and resonating chambers nor the traditional and often preferred tri-flow design. Furthermore, the conventional tubes disposed in the stamped chambers are perforated to achieve communication between the exhaust gas of the tube and the chamber. Japanese Published Patent Application No. 59-43456 shows a muffler with stamped components and conventional tubes, including a tuning tube and low frequency resonating chamber. However, the muffler shown in Japanese Published Patent Application No. 59-43456 does not include the tri-flow pattern that is desireable in many exhaust systems, and the chamber is at an off-line location in the muffler.
Substantial improvements in stamped muffler technology have been made in recent years. In particular, re-issue U.S. Pat. No. RE33,370 and reexamined U.S. Pat. No. 4,736,817 show mufflers formed entirely from stamped components and including at least one expansion chamber, at least one low frequency resonating chamber and tuning tube combination and/or a high frequency tuning chamber. Mufflers incorporating the teaching of re-issue U.S. Pat. No. RE33,370 and U.S. Pat. No. 4,736,817 achieve all of the functional and manufacturing advantages of stamped mufflers and are able to equal or exceed the performance of conventional mufflers. In view of the many advantages, the stamp formed mufflers shown in re-issue U.S. Pat. No. RE33,370 and U.S. Pat. No. 4,736,817 have achieved very substantial commercial success.
The assignee of re-issue U.S. Pat. No. RE33,370 and U.S. Pat. No. 4,736,817 is the assignee of the subject invention and has made other substantial improvements in stamped muffler technology. For example, U.S. Pat. No. 4,901,816 and U.S. Pat. No. 4,905,791 both issued to David Garey and show mufflers formed only from two stamped external shells and with the tail pipe and exhaust pipe of the system extending into the outer shell for contributing to the noise attenuation carried out by the muffler. More particularly, the outer shell is stamped to define baffles for supporting portions of the exhaust pipe and tail pipe disposed within the muffler. End regions of the exhaust pipe and tail pipe are provided with perforations or louvers to enable a controlled expansion of exhaust gas into certain of the chambers defined by the external shell. The muffler shown in U.S. Pat. No. 4,759,423 is light weight and offers several cost efficiencies. However, tuning options may be limited as compared to other mufflers developed by the assignee of the subject invention.
U.S. Pat. No. 4,759,423 issued to Harwood et al. on Jul. 26, 1988 and is assigned to the assignee of the subject invention. U.S. Pat. No. 4,759,423 shows a tri-flow muffler with a reversing chamber defined by an external shell and disposed at one end of the muffler. A tuning tube and low frequency resonating chamber are disposed at the opposed end of the muffler, but are not disposed for a "driven" tuning. The muffler shown in U.S. Pat. No. 4,759,423 is substantially identical to the muffler shown in the above referenced U.S. Pat. No. 5,012,891. However, U.S. Pat. No. 4,759,423 is effective in eliminating at least some of the low frequency noise that presumably is considered desireable in U.S. Pat. No. 5,012,891.
Many of the mufflers shown in the above-referenced patents that are assigned to the assignee of the subject application include baffle creases in the external shells to separate one chamber from another. In particular, the baffle creases in the external shell extend a sufficient depth for the base of the baffle crease to contact an opposed region of a stamp formed internal plate. Mufflers formed with baffle creases in the external shell necessarily require a drawing of substantial amounts of metallic material, and hence can increase the total amount of metal required for the external shell. It also has been suggested that baffle creases could create pockets in which corrosive materials could accumulate. This alleged potential for corrosion of stamp formed mufflers in the vicinity of baffle creases has not been observed in tests performed to date. However, there of course is a desire to avoid even a suggestion for such a problem. Furthermore, mufflers requiring plural low frequency resonating chambers with corresponding tuning tubes and with high frequency tuning chambers could lead to very complex draws of metal in the external shell that might be difficult to achieve without excessive stretching of the metal.
U.S. Pat. No. 5,004,069 issued to Van Blaircum et al. on Apr. 2, 1991 and also is assigned to the assignee of the subject application. U.S. Pat. No. 5,004,069 shows a muffler that employs a transversely aligned tube which functions as a baffle between chambers of the muffler. The use of a transverse baffle tube avoids the formation of a deeply drawn baffle crease in an external shell of a muffler. Although the muffler shown in U.S. Pat. No. 5,004,069 includes tuning tubes and low frequency resonating chambers, the design does not show placement of the tuning tubes and low frequency resonating chambers for achieving a "driven" tuning. U.S. Pat. No. 5,004,069 also does not show the tri-flow design which is desireable in many situations.
U.S. Pat. No. 4,860,853 issued to Walter G. Moring III on Aug. 29, 1989 and also is assigned to the assignee of the subject invention. U.S. Pat. No. 4,860,853 shows a muffler that achieves substantial cost and weight efficiencies in that it can be formed with only three stamped components. The muffler of U.S. Pat. No. 4,860,853 also avoids the formation of pockets on at least upwardly facing surfaces of the muffler. However, certain deep draws of metal may be required for at least certain embodiments of the muffler depicted in U.S. Pat. No. 4,860,853.
U.S. Pat. No. 4,847,965 issued to Harwood et al. on Jul. 18, 1989 and also is assigned to the assignee of the subject invention. U.S. Pat. No. 4,847,965 shows a method of manufacturing stamp formed mufflers where die inserts are employed in the stamping equipment to enable selective variations to be made in the stamp formed components to accommodate the needs of certain vehicles within a family of related vehicles and without employing an entirely new set of master dies. As a result, a system of mufflers may be formed having generally the same pattern of tubes therein, but with selected portions of tubes in one muffler being different from comparable sections in another muffler to enable the respective mufflers to perform slightly different acoustical functions.
Co-pending application Ser. No. 577,495 was filed on Sep. 4, 1990 by Michael Clegg et al. and shows a stamp formed muffler with flow tubes and in-line expansion chambers dimensioned to achieve expansion ratios that optimize noise attenuation.
The disclosures of the prior art patents and the pending application assigned to the assignee of the subject invention are incorporated herein by reference.
Still another prior art stamp formed muffler is shown in U.S. Pat. No. 5,012,891 which issued to Macaluso on May 7, 1991. U.S. Pat. No. 5,012,891 shows a muffler with opposed plates formed to define tubes and opposed pan shaped halves formed to define an outer shell surrounding the tubes. A conventional tube extends through a turn around or reversing chamber defined by the pan shaped halves and connects to the tubes formed by the plates. In one embodiment, exhaust gas entering the turn around chamber of U.S. Pat. No. 5,012,891 flows under and over the conventional tube while flowing toward the return tube, as had been the case with the typical prior art muffler 10 shown in FIG. 9. Also like the conventional muffler shown in FIG. 9, the turn around chamber of the muffler of U.S. Pat. No. 5,012,891 is defined by substantially parallel opposed walls which are substantially orthogonal to the plane defined by the connected plates.
Despite the many advantages in stamped muffler technology achieved by the assignee of the subject invention, there is a desire to further improve stamped mufflers. In particular, it is desired to substantially increase the tuning options available with stamped mufflers without necessarily complicating the individual stamped components and without creating large draws of metal in the external shell.
In view of the above, it is an object of the subject invention to provide a formed muffler that provides efficiently configured in-line flow tubes and in-line expansion chambers to reduce flow noise and back pressure.
It is another object of the subject invention to provide a formed muffler that avoids deep draws of metal and the creation of pockets in the external shells.
It is a further object of the subject invention to provide a formed muffler with at least one low frequency resonating chamber and at least one driven tuning tube.
Still a further object of the subject invention is to provide a family of related mufflers with certain members of the family having high frequency tuning capability.
Yet another object of the subject invention is to provide a tri-flow muffler with at least one driven tuning tube and low frequency resonating chamber.
An additional object of the subject invention is to provide a tri-flow muffler with a reversing chamber defined by internal plates and insulated from the external shell to avoid shell ring.
A further object of the invention is to provide a muffler that can achieve efficient tuning with only three formed components.